Here is my idea. Set the timer interrupt to 874hz (period value of 7). During interrupt routine, stuff 32 PCM samples into the pattern buffer of channel 0, reset timer. On next interrupt, start playing channel 0 at 874hz (period value 127) and then stuff the next 32 PCM samples into the pattern buffer of channel 1. Third interrupt, start playing channel 1, reload channel 0, etc.

So basically, using two channels for double buffering of samples, loading 32 samples per interrupt, and playing PCM audio at 27965hz.